An exterior car modification in which you replace the stock bumpers and side skirts with after market ones. Most of the time its purely aesthetic to make your car "faster". But, if your not a stupid teenager, some body kits are actually aerodynamic and CAN add some speed to your car. The amount is small though.

Guy1: I just got this sick lookin' body kit.
Guy2: Dude, It looks like a rice burner.

A body kit is a collection of exterior modifications to a car, typically comprised of front and rear bumpers (fenders), side skirts, and spoilers. Companies sell these replacements as alternatives to the traditional look of the vehicle from the factory. Body kits will be designed to complement each other, and work together as a complete design. Despite this, the 'mix and match' approach is often seen on cars, where the front of one kit will be matched with the rear of another.

Automative body kits are usually constructed of either fiberglass or polyurethane. Most car modification entusiasts prefer polyurethane because it is more resistant to damage, and does not crack in cold weather. In some cases, body kits may also be constructed of carbon fiber, which is a popular, lightweight material. This type of modification is not as highly regarded among speed enthusiasts, though, because it is very costly, and the difference in weight is minimal, versus changing other parts such as the hood or trunk.

Factory fitted bodykits are now becoming more common, perhaps in response to the growth of the aftermarket tuning industry in the late nineties and onwards.

Most are lame and ugly exaggerated bumpers on cars made to give teenagers the illusion that it is lowered. These are extremely useless and degrade the overall image of the car.

On the other hand there are body kits that are actually useful to the car and not ugly. These kinds are all mostly made by JDM Part companies such as TRD, Mazdaspeed, and Nismo. The body kits are produced by these companies to actually make use of aerodynamics while being able to preserve the car's beauty.